The worst case would be if ebay says he can return it to you for a refund. So he will return it to you at his cost and you will refund him all the money he paid (ie. you will make a loss on fees and original p&p).
His move![]()
Except that's not worst case when he sends an 'identical' bust part back which cannot be sold on. He has lost fees, postage costs and his item. That's kind of the issue at hand here...well - potentially.